This invention relates to thin rubber sheeting or membranes useful for covering roofs of building structures. In particular, the rubber sheeting of this invention includes an integral adhesive on the edges which can be used to adhere adjacent sheets to one another to form a water-tight geomembrane. The membrane is useful in roofing as well as pond linings, tank linings and other applications where relatively thin rubber sheeting is used to protect a surface from its environment.
The long standing problem in roofing and lining applications is the establishment of strong water-tight seams between adjacent rubber sheets. Ethylene-propylene based thermosetting rubbers such as EPDM and EPM type rubbers are very weather-resistant but are long recognized to be difficult to adhesively bond together. The seams must be capable of withstanding the environmental stresses placed on the sheeting during high winds, heavy rains, snows, ice storms. Flat roofs pose unique problems to roofing membranes. Due to inevitable variability the plane of the roofing structure, low areas will be formed which allow the formation of standing water pools. These pools when frozen and unfrozen place constant stress on the seams between the rubber sheet. Any flaw in the seam will potentially allow water ingress. In addition, during the service life of the roof, which may exceed twenty years, there is the probability of substantial foot traffic over the roofing membrane which creates stresses on the sheeting interface seams. Prior to this invention the most dependable method for seaming the rubber sheets involved a multi-step process for preparing the edges of the rubber sheets for adhesive seaming. First solvents are used to clean off contaminants from the portion of the sheet immediately adjacent the edge used for the lap-splice. These contaminants include dirt, dust, talc, oils and components of the rubber formulation which exude to the surface of the rubber sheet. After solvent cleaning, an adhesive primer is preferably applied to the cleaned edge. The primer typically must be allowed to dry for some period of time. Subsequent to the application of the primer, a solvent-based or liquid adhesive is applied to the edge portions which are to be overlap spliced. The type of adhesive used determines the treatment. If a solvent-based contact adhesive is used, the edge is allowed to dry to the touch prior to overlapping. Full bond strengths may require several weeks to develop. If an air-cure urethane adhesive is used, the edge is immediately overlapped and then allowed to stand undisturbed for a period of time ranging from several hours to several days to allow the adhesive to set up and attain its full bonding strength. A caulk must then be applied to the overlapped edge of the seam in order to protect the adhesive from the attack of water which infiltrates the seam. Of course, over the many years of service the caulk barrier must be renewed to assure seam integrity. This multi-step adhesive process is very labor-intensive and requires handling the same edge portion to be seamed several times during the bonding process. The problems associated with the current adhesive system include (1) its labor and time intensive application methods and (2) the method requires the use of volatile and potentially hazardous solvents, primers and adhesives. The bonds obtained during the seaming process may be (a) inconsistent or flawed due to failure to properly clean the edge: (b) application of a non-uniform adhesive layer: (c) making the overlap seal before sufficient solvent had flashed out of the adhesive (adhesive too tacky): (d) waiting too long after application of adhesive to make the overlap seam (adhesive too dry); and (e) insufficient or non-uniform application of pressure after the seam is made.
It has been surprisingly and unexpectedly found that certain polyolefins function as superior thermoplastic adhesives for bonding ethylene-propylene based rubber sheets to each other. These adhesives surprisingly do not exhibit any adhesive properties when applied and cured with other types of thermosetting rubber polymers. The many disadvantages and poor economics of these previously known systems for splicing EPDM rubber sheeting to roofs are overcome by the use of this invention. It is an object of the invention to provide an environmentally safe adhesive system which eliminates the use of solvents, chemicals and primers. A further object is to provide a simple one step system for seaming adjacent rubber sheets into a water-impervious seam. Another object of the invention is to provide an adhesive which may be applied to the rubber sheeting during its manufacture and supplied for the roofing installation with the adhesive as an integral part of the rubber sheet. An advantage of the adhesive system utilized for the rubber sheeting of this invention is that maximum bond strength is developed within seconds of making the actual splice. A further advantage of the invention is that the adhesive is unaffected by water and adverse environmental conditions in a roofing installation. The adhesive is intimately bonded to the rubber sheeting membrane to provide a very high bond strength.